Polyphase electricturning machine such as an alternator or an alterno-starter, particular for a motor vehicle

ABSTRACT

A polyphase electric turning machine such as an alternator or an alterno-starter, particularly for a motor vehicle. The machine comprises a stator surrounding a rotor inside a case; the stator comprises a three-phase star-shaped winding and a triangular three-phase winding whose outputs are connected to rectifier bridges which are parallel mounted between the ground and a common output terminal. The two windings are received together in the recesses of the stator. The number of star-shaped winding spires and triangular winding spires in the machine is selected in such a way that the number of spires of each winding is respectively 3.

FIELD OF THE INVENTION

The invention concerns a multiphase rotary electrical machine such as analternator or alternator/starter, in particular for a motor vehicle, ofthe type comprising, within a casing, a stator surrounding a rotor, thestator comprising a three-phase star winding and a three-phase deltawinding, the outputs of which are connected to bridge rectifiersconnected in parallel between earth and the output terminal of therotary electrical machine, the two windings being received together inrecesses in the stator.

These two three-phase windings, one connected in a star, the otherconnected in a delta, form a composite winding stator device.

BACKGROUND OF THE INVENTION

A rotary electrical machine of this type is known through the Frenchpatent number 2 737 063, to which reference can be made for moredetails. So that the voltages produced by the two three-phase windings,one connected in a star and the other connected in a delta, areidentical, it is indicated that the turns of the delta winding must be√3 times the number of the turns on the star winding. It is also statedthat the ratio of the cross sections of the turns of the two windingsmust be 1/√3.

The prior art is thus limited to stating a few specific positive effectsprocured by the composite winding stator device.

SUMMARY OF THE INVENTION

The aim of the invention is to go further by proposing possibilities foroptimising the performance of a rotary electrical machine as definedabove, by virtue of the composite winding stator device.

To achieve this aim, the rotary electrical machine according to theinvention in which the ratio of the number of turns of the star anddelta windings is chosen so that the number of turns in each winding areinteger numbers, whilst keeping the ratio of these numbers as close aspossible to √3, is characterised in that the number of turns on the starwinding and the number of turns on the delta winding are respectively 3and 5.

According to yet another characteristic, the diameter of the wire in thestar winding is different from the wire in the delta winding and theratio of the diameters is chosen so as to be close to the optimum ratioof √3 of the resistances of the windings, and the diameters of the starand delta stator windings are chosen so as to obtain a fill factor ofthe recesses greater than 50%.

According to yet another characteristic of the invention, the starwindings formed by two wires in parallel, advantageously wound indistributed mode.

According to yet another advantageous characteristic of the invention,the turns of the star winding of a stator recess are disposed at therecess opening, distributed, whilst the turns on the delta winding arein the bottom of the recess.

According to yet another advantageous characteristic of the invention,in a rotor comprising pairs of poles and permanent magnets, the numberof magnets is less than the number of poles and the magnets are disposedsymmetrically at the centre of the rotor.

Naturally these advantageous characteristics can be considered inisolation or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood better, and other aims,characteristics, details and advantages thereof will emerge more clearlyin the course of the following explanatory description made withreference to the accompanying drawings given solely by way of exampleillustrating one embodiment of the invention and in which:

FIG. 1 is a view in axial section of a rotary electrical machine of theprior art;

FIG. 2 illustrates the electrical diagram of a rotary electrical machinewhere the stator winding comprises a three-phase star winding and athree-phase delta winding, according to the prior art;

FIG. 3 is a view in section, with cutaway, of the stator of a rotaryelectrical machine according to the invention;

FIG. 4 is a perspective view of a rotor of a rotary electrical machineaccording to the invention; and

FIG. 5 is a curve representing the thermal state T of the machine as afunction of the ratio R of the numbers of turns on the star and deltawindings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a rotary electrical machine is described belowbriefly, in the present case an alternator here of the three-phase type,in particular for a motor vehicle with a thermal engine, of the priorart, to which the invention is applicable. Naturally the alternator canbe reversible and consist of an alternator/starter in particular forstarting the thermal engine of the vehicle. When the machine isfunctioning in alternator mode it transforms mechanical energy intoelectrical energy like any alternator. When the machine is functioningin electric motor mode, in particular in starter mode for starting thethermal engine of the motor vehicle, it transforms electrical energyinto mechanical energy.

This machine comprises essentially a casing 1 and, inside it, a rotor 2rotationally fixed to a shaft 3 and a stator 4 which surrounds the rotorand comprises a body in the form of a packet of metal sheets providedwith recesses, here of the semi-closed type, for mounting statorwindings forming on each side of it a leading-out wire indicated at 5.These windings comprise here a three-phase star winding and athree-phase delta winding arranged as described below so as to form acomposite winding stator device.

The rotor is produced in the example depicted in the form of a clawrotor, as described for example in the documents US 2002/0175589 A1 andEP 0 454 039 A1, comprising two pole wheels 7, 8 axially juxtaposed andeach having a transfer flange provided at its external periphery withtrapezoidal-shaped teeth 9 directed axially towards the flange of theother pole wheel, the tooth of one pole wheel entering the space betweentwo adjacent teeth 9 on the other pole wheel, so that the teeth on thepole wheels are interlocked. An excitation winding 10 is located axiallybetween the flanges and the pole wheels 7, 8. It is carried by a rotorpart in the form of a cylindrical core, which could be distinct from theflanges or be in two parts each belonging to one of the flanges asdepicted in FIG. 1. When the excitation winding 10 is activated, that isto say electrically supplied, the rotor made from ferromagnetic materialis magnetised and becomes an inductor rotor with the formation ofmagnetic poles at the teeth on the pole wheels.

This inductor rotor creates an induced alternating current in thearmature stator when the shaft 3 rotates.

In a variant, the rotor can be of the projecting pole type, as describedfor example in WO 02/054566, and then comprises several excitationwindings each wound round such a pole.

The shaft 3 of the rotor 2 carries at its front end a pulley 12belonging to a movement transmission device with at least one beltbetween the alternator and the thermal engine of the motor vehicle andat its rear end 13 collector rings connected by cabled connections tothe ends of the excitation windings of the rotor. Brushes belong to abrush holder depicted in a general fashion at 14 and are disposed so asto rub on the collector rings. The brush holder is connected to avoltage regulator.

The casing 1 is in two parts, namely a front bearing 16 adjacent to thepulley 12 and a rear bearing 17 carrying the brush holder, the voltageregulator and bridge rectifiers described below. The bearings are hollowin shape and each comprise centrally a ball bearing respectively 19 and20 for the rotational mounting of the shaft 2 of the rotor 3. Thebearings are, in the machine shown, perforated so as to allow thecooling of the alternator by the circulation of air. To this end, therotor carries at least at one of its axial ends a fan intended toprovide this circulation of air. In the example depicted, a fan denoted23 is provided on the front face of the rotor and another fan 24, morepowerful, at the rear face, each fan being provided with a plurality ofblades indicated at 25 and 26. In a variant, the alternator can becooled by water, the casing then being configured so as to comprise asuitable water circulation channel.

A rotary electrical machine of the type depicted in FIG. 2 and to whichthe invention is applicable comprises a composite winding stator devicewhich comprises, as depicted in FIG. 2, a three-phase star winding 28and a three-phase delta winding 29, the outputs of which are connectedto bridge rectifiers respectively 30 and 31 comprising rectifyingelements such as diodes 32 or transistors of the MOSFET type, inparticular when the machine is of the reversible type and consists of analternator/starter as described for example in the document FR A 2 745445 (U.S. Pat. No. 6,002,219).

Thus (FIG. 2) each three-phase winding comprises three arms eachconsisting a winding of a phase.

The three-phase star winding comprises three arms connected in a starand therefore a common input and three outputs electrically connected tothe bridge 30.

The three-phase delta winding comprises three arms connected in atriangle, that is to say electrically connected in pairs to each of thevertices of the triangle. Each vertex constituting an input. The outputsof this three-phase winding are electrically connected to the bridge 31.

The bridge rectifiers are connected in parallel between earth and the DCoutput terminal 33.

These bridges are carried by the rear bearing 17 of the alternator, ascan be seen for example in FIG. 3 of the document FR A 2 737 063.

The bridges are full-wave bridges of the Graetz type. These bridges makeit possible in particular to rectify the alternating current produced inthe windings of the stator into DC current, in particular to charge thebattery of the motor vehicle.

So that the voltages delivered by the two windings are substantiallyidentical, the number of turns on the delta winding 29 is √3 timesgreater than the number of turns on the star winding 28. The ratiobetween the cross sections of the turns on the delta winding and theturns on the star winding is 1/√3.

Given that the diagram in FIG. 2 is known, for example through Frenchpatent number 2 737 063, it will not be described below in any furtherdetail.

As can be seen in FIG. 3, the turns on the star 28 and delta 29 windingsare disposed in the same recesses denoted 35, the turns on the deltawinding being placed close to the opening 36 of the recesses, whilst theturns of the star winding 28 are placed in the bottom.

It should be noted that, in the example embodiment described, the rotor2 (FIG. 4) comprises eight teeth 9 per pole wheel and therefore eightpairs of poles. There are therefore provided 48 recesses in the body ofthe stator, that is to say half the number of notches as in the solutiondescribed in the aforesaid documents US 2002/0175589 A1 and EP 0 454 039A1. Naturally the rotor can, according to the applications, comprise 6,7, 10 or 12 pairs of poles and the stator 36, 42, 60 or 72 pairs ofpoles.

In a known fashion, it being a case of a three-phase winding between twosuccessive recesses receiving a first arm of the winding, two recessesare provided for receiving respectively the second and third arm of thewinding.

It should also be noted that each recess 35 comprises, in a knownmanner, a recess insulator, not referenced, in order to insulate thewires of the windings with respect to the body of the stator, and thatthe opening 36 of each recess 35 is sufficiently wide to allow the wiresof the windings to pass. This entrance is, in a known manner, closed bya recess chock, not referenced. This chock is advantageously elastic inorder to exert a clamping action on the wires of the windings.

The aim of the invention is to improve rotary electrical machines of thetype shown in FIGS. 1 and 2 by optimising their performance, inparticular by virtue of a suitable configuration of the compositewinding stator device, and additional constructional measures, as willbe described below.

The invention is essentially based on the discovery that the choice ofthe number of turns received in each recess of the stator, of the star28 and delta 29 windings, have a considerable impact on the performanceof the machine.

In the context of the invention, it has been found that, in order toobtain optimum thermal conditions, the number of turns must be as smallas possible but that the ratio of the number of turns of the deltawinding with respect to the turns on the star winding must be as closeas possible to the optimum value of √3.

Measurements have established the characteristic curve shown in FIG. 5,which indicates on the Y-axis the thermal state of the machine, namelythe temperature measured on the iron of the stator body, that is to sayon the packet of metal sheets constituting the body of the stator, or atthe diodes of the bridge rectifiers, and on the X-axis the ratio R ofthe number of turns on the two windings. The X-axis also carries variousratios or pairs of turns that can be envisaged according to the twoconditions and taking into account the fact that each number of turnsmust be an integer number. Thus the X-axis carries the ratios that canbe envisaged for numbers of turns on the star winding 2, 3, 4. It can beseen that the curve has the form of a bell opening towards the top, witha minimum value between the ratios 5/3 and 7/4, where the ratio of theoptimum value is √3. The thermal degradation to the right of the value√3 when the number of turns on the star winding increases is explainedby the fact that the leading-out wire, which has then become large, doesnot allow the cooling air to pass, which has been able to be measured inthe form of an increase in the temperature of the stator ion. To theleft of the value √3 the thermal situation degrades because, for anumber of star winding turns equal to 2, it is necessary to associatefour delta winding turns, which gives rise to a ratio of 2 instead ofthe optimum ratio √3. This ratio far different from the optimum valuecauses an imbalance in the electrical system, which manifests in theform of an increase in the temperatures at the diodes of the bridgerectifiers.

Consequently, it has turned out that a winding configuration comprisingin each recess three star winding turns and five delta winding turns isparticularly advantageous.

It was indicated above that the composite winding stator device, that isto say partly star and partly delta, must also comply with theconditions that the ratio of the resistance of the delta winding must beequal to the resistance of the star winding multiplied by 1/√3. In orderto get close to this optimum ratio of 1/√3, the invention proposes touse delta winding and star winding wires of different diameters. Anoptimisation of the thermal conditions under which the machine canfunction is obtained if it is ensured that the fill coefficient of therecess is greater than or equal to 50%, and the diameters of the wiresis as large as possible in order to ensure good ventilation of theleading-out wires. However, given that the fitting of the turns in therecesses is easier for wires with a smaller diameter, provision is madeto produce the turns of the star winding by means of parallel wires.However, the number of parallel wires must be as small as possible inorder to ensure good ventilation of the leading-out wires.

It has proved, in the context of the invention, to be particularlyadvantageous to produce the three-phase winding in delta mode, that isto say each arm of this winding with a wire with a first diameter, andthe three-phase winding in star mode, that is to say each arm of thiswinding with two wires in parallel with a second diameter wound indistributed mode. For the record it should be stated that a winding indistributed mode consists of winding the wire in the recesses of thestator body in one circumferential direction and then, after one turn ofthe stator body, winding the wire in the recesses of the stator body inthe other circumferential direction.

Here, with the star winding, for each arm thereof, three turns of thestator body are made in the notches thereof with two wires in parallel,that is to say two wires in hand, and with the delta winding five turnsof the stator body are made in the notches thereof.

Each arm therefore comprises respectively three and five turns.

By applying this arrangement to the particularly advantageous pair offive three-phase delta winding turns and three three-phase star windingturns in each recess of the stator, the configuration shown in FIG. 3 isobtained with six wires of a star winding arm, at two wires per turn, atthe bottom of the recess under the five turns, that is to say the fivewires, of a delta winding arm.

By way of example, in a composite winding stator device without parallelwire arrangements, the delta winding could be produced with a 1.6 mmwire and the star winding with a 2.24 mm wire. The production inparallel of the turns of the star winding could allow the use, for thestar winding wires and the dealt winding wires, of wires with diametersrespectively of 1.6 mm and 1.7 mm.

It should be noted that the arrangement of the delta winding wires closeto the opening 36 of the recesses 35 and the star winding wires in thebottom of the recesses provides a good balance in terms of electricaloutput. However, in order to improve the thermal conditions and toreduce the noise of the machine, it is advantageous to place the starwinding wires at the opening of the recesses, in distributed mode, asthe delta winding wires at the bottom of the recesses.

The performance, namely the power and the efficiency, of a machineaccording to the invention can be increased further by using a rotorhaving the configuration according to FIG. 4. This rotor comprises, in afashion known per se and for example described in French patent number 2784 248, interposed between two adjacent teeth 9 at the periphery of thestator such as the stator 2 according to FIG. 1, a certain number ofpermanent magnets 38, choosing the number of these magnets so that it isless than the number of rotor poles and so that their arrangement issymmetrical with respect to the axis of the rotor. This provision of theinvention is also applicable to rotors of the projecting pole type.

In FIG. 4 four pairs of magnets 8 for eight pairs poles are provided.

It should be noted that it is also advantageous in the context of theinvention to provide, at the external periphery of the stator body, inthe form of a packet of metal sheets, an elastic system for filteringthe vibrations, with, in front, a flat seal 40 and, at the rear, pads41, flexible heat-conductive resin being interposed between the frontbearing and the body of the stator in order to discharge the heat, ascan be seen in FIG. 1.

It is clear from the above description that the invention procures,compared with the prior art, many advantages, such as an improvement inthe specific output, a reduction in magnetic noise and in the ripplefactor. These advantages are obtained by virtue of the offset of 30electrical degrees between the two star and delta windings in the statorwhilst complying with a ratio of the number of turns of √3 and a ratioin the resistance of the windings of 1/√3. The machine is in FIG. 1cooled by air by a front fan and a more powerful rear fan. The power ofthe machine can also be increased by using higher performance fans suchas fans obtained by the superimposition of two unit fans each comprisinga series of blades as described for example in the document FR A 2 741912 and as can be seen in FIG. 1 (rear fan). The diameter of the wire ofthe star winding is different from the diameter of the wire of the deltawinding. The star winding could be wound with two wires in hand and thedelta winding with one wire in hand. The star winding is wound indistributed mode and the wires used are round wires in order to improvethe cooling of the leading-out wires of the stator. A cross section ofthe wire is greater than or equal to 1.5 mm. The position of the phasesin the leading-out wire could be alternated.

In order to improve further the cooling of the leading-out wires,windings with a different axial height at the leading-out wires areprovided. Thus one of the windings, preferably the one situated close tothe bottoms of the recesses, extends in axial projection with respect tothe other winding at each leading-out wire. In this case, the starwinding is placed in the bottom of the recesses.

1. A multiphase rotary electrical machine comprising: bridge rectifiers;a stator disposed within a casing, the stator comprising a stator bodyhaving recesses: and a rotor surrounded by the stator; the statorfurther comprising a three-phase star winding and a three-phase deltawinding, the outputs of the star winding and three-phase delta windingbeing connected to the bridge rectifiers connected to each other inparallel between earth and a common output terminal; the two windingsbeing received together in the recesses in the stator body; the ratio ofthe number of turns of the windings in the star winding and the deltawinding is chosen so that the number of turns in each winding is aninteger number, whilst keeping the ratio of these numbers of turns asclose as possible to √3 and as small as possible; wherein the number ofturns on the star winding and the number of turns on the delta windingare respectively 3 and 5, wherein the diameter of the wire in the starwinding is different from the diameter of the wire in the delta windingsuch that the diameters are chosen so that the ratio of the transversesections of the two windings is close to the value √3, and such that thediameters of the star and delta stator windings are chosen so as toobtain a fill factor of the recesses in the stator greater than 50%, andwherein the star winding is formed by two wires in parallel wound indistributed mode.
 2. A multiphase rotary electrical machine comprising:bridge rectifiers; a stator disposed within a casing, the statorcomprising a stator body having recesses: and a rotor surrounded by thestator; the stator further comprising a thee-phase star winding and athree-phase delta winding, the outputs of the star winding andthee-phase delta winding being connected to The bridge rectifiersconnected to each other in parallel between earth and a common outputterminal; the two windings being received together in the recesses inthe stator body; the ratio of the number of turns of the windings in thestar winding and The delta winding is chosen so that the number of turnsin each winding is an integer number, whilst keeping the ratio of thesenumbers of turns as close as possible to √3 and as small as possible;wherein the number of turns on the star winding and the number of turnson the delta winding are respectively 3 and 5, and wherein the turns onthe star winding in a stator recess are disposed at the opening of therecess in distributed mode, whilst the turns on the delta winding aresituated in the bottom of the recess.
 3. The machine according to claim2, wherein the diameter of the wire in the star winding is differentfrom the diameter of the wire in the delta winding such that thediameters are chosen so that the ratio of the transverse sections of thetwo windings is close to the value √3, and such that the diameters ofthe star and delta stator windings are chosen so as to obtain a fillfactor of the recesses in the stator greater than 50%.
 4. The machineaccording to claim 2, wherein the diameter of the wire in the starwinding is different from the diameter of the wire in the delta windingsuch that the diameters are chosen so that the ratio of the transversesections of the two windings is close to the value √3, and such that thediameters of the star and delta stator windings are chosen so as toobtain a fill factor of the recesses in the stator greater than 50%, andwherein the star winding is formed by two wires in parallel wound indistributed mode.